This invention relates to a wiring substrate comprising a wiring substrate with a wiring pattern formed thereon, a gas discharge display device using the same, and a method therefor.
Gas discharge display devices such as plasma display and the like make display through a self-luminescence, and therefore are characterized in that the field angle is large, the display is easy to see, the thickness can be lessened, and a large picture plane can be realized. Thus, such gas discharge display devices have become applied to display devices of information terminal equipments and high-quality picture tubes of television. Plasma displays are roughly classified into direct current driving type and alternate current driving type. Among them, the alternate current type of plasma display shows a high luminance owing to the memory action of dielectric layer covering electrodes, and its lifetime has reached a practical level through formation of protective layer. This results in practical application of plasma displays to video monitors for many uses.
FIG. 9 is a perspective view illustrating the structure of a practical plasma display panel, wherein the front side substrate 100 is shown apart from the back side substrate 200 for the purpose of facilitating understanding.
The front side substrate 100 comprises a display electrode 600 made of a transparent conductive material such as ITO (indium tin oxide), tin oxide (SnO2) or the like, a bus electrode 700 made of a low-resistance material, a dielectric layer 800 made of a transparent insulating material and a protecting layer 900 made of magnesium oxide (MgO) or the like, all being formed on a front side glass substrate 400.
The back side substrate 200 comprises an address electrode 1000, a barrier rib 1100 and a fluorescent material layer 1200, all formed on a back side glass substrate 500. Although not shown in FIG. 9, a dielectric layer 1300 is formed on the address electrode 1000, too.
By affixing the front side substrate 100 to the back side substrate 200 so that the display electrode 600 makes an approximately right angle with the address electrode 1000, a discharge space region 300 is formed between the front side substrate 100 and the back glass side substrate 500.
In this gas discharge display device, an alternate current voltage is applied between one pair of display electrodes 600 provided on the front side substrate 100, and a voltage is applied between the address electrode 1000 provided on the back side substrate 200 and the display electrode 600, whereby an address discharge is made to occur and a main discharge is generated in a prescribed discharging cell. The main discharge generates an ultraviolet ray, which induces emission of lights from the red-, green- and blue-color fluorescent materials 1200 separately coated on respective discharging cells. A display is made by emission of these lights.
Examples of such prior gas discharge display devices are described in, for instance, FLAT PANEL DISPLAY 1996 (Edited by Nikkei Microdevice, 1995), pages 208-215.
Here, the method for forming the bus electrode 700 carried on the front side substrate 100 and the address electrode 1000 carried on the back side substrate 200 will be mentioned below in more detail. FIGS. 5, 8A-8O illustrate an exemplary process for forming address electrode 1000 on back side glass substrate 500. Explanation of the process for forming bus electrode 700 carried on front side substrate 100 is omitted, because it can be formed by a similar process.
First, a Cr/Cu/Cr layer (1000a-c) for forming address electrode 1000 on the back side glass substrate 500 and a resist 2500 for forming the pattern of address electrode 1000 are successively piled lamination-wise by a film-forming technique such as sputtering, evaporation, spin coating, dry filling, etc. (Step (a), FIG. 8A: Film forming step). Next, the resist 2500 is exposed to light and developed so as to form a desired pattern of address electrode 1000 (Steps (b) and (c), FIGS. 8B and 8C: Photolithographic step). Next, using an etching solution for Cr, the Cr layer 1000a is etched to form the desired pattern (Step (d), FIG. 8D: Etching step). Next, the exposed and developed resist 2500 is peeled off, and a resist 2500 is again formed (Steps (e) and (f), FIGS. 8E and 8F). The above-mentioned treatments are repeated for each of Cu layer 1000b and Cr-layer 1000c (Steps (g) to (o), FIGS. 8G-8O). Thus, address electrode 1000 is formed on the back side glass substrate 500.
The above-mentioned process using an etching solution is generally called xe2x80x9cwet etchingxe2x80x9d. In the conventional wet etching processes, the resist 2500 is formed from an organic material.
Further, in the conventional formation of electrodes by wet etching, a photolithographic step for forming a resist is indispensable.
In order to reduce the number of repetition of the photolithographic steps, the present inventors have studied on a technique for forming a multi-layered wiring such as those having a structure of Cr layer 1000a/Cu layer 1000b/Cr layer 1000c, etc. by using only the resist 2500 formed by Steps (a)-(c). This technique may be realizable if an etching solution capable of selectively etching Cr layer or Cu layer is used. Actually, however, it has experimentally been revealed that Cr layers 1000a and 1000c are quite readily side-etched and accuracy of fabrication of the Cr/Cu/Cr layer is quite unstable, so far as an etching solution giving no damage to alkali-developable releasable resists is used. If a Cr layer is side-etched, the side-etched portions form gaps, which incurs inclusion of voids and contaminants such as etching solution. The contaminants cause corrosion and breakage of wiring in the step of firing the dielectric. Occurrence of breakage in the wiring means existence of wire portions not contributing to display in a gas discharge display panel, which is a fatal problem to a display panel. Since Cr/Cu/Cr layer constitutes a wiring of lower resistance as compared with other electrode materials, it is quite useful for large-sized display devices such as gas discharge display panel and the like. But, the same problem as mentioned above arises also in case of forming a multilayer wiring such as Cr/Al/Cr by the method of wet etching.
Further, if the resist is formed of an organic material, the adhesion between resist and electrode is insufficient, which causes corrosion by etching solution at the resist interface. It has further been revealed that, in such a resist, extraneous materials and air bubbles are included to cause defects in resist, due to which corrosion and thereby caused breakage of wiring can occur. Further, since conventional resists have been formed by a photolithographic process, they are apt to have defects due to extraneous matter. If electrode is formed by wet etching from a resist including defects, the regions corresponding to the defects are similarly etched, which causes breakage of wiring. These problems arise not only in Cr/Cu/Cr type multi-layer wiring, but also in case of forming a wiring of Al, Ag, Ni, Au, etc. by wet etching.
As above, in the gas discharge display panels and wiring substrates in which electrodes are formed by the conventional wet etching technique, breakage of wiring has readily occurred due to side-etching of electrode and unexpected corrosion. Further, breakage of wiring due to defects of resist has also been apt to occur.
It is an object of this invention to suppress the breakage of wiring in the electrodes formed in wiring substrates and gas discharge display panels. In particular, the object of this invention consists in suppressing the breakage of wiring in the case of forming electrodes by wet etching process.
In order to achieve the object mentioned above, this invention forms a resist from an inorganic material in a wet etching process.
Thus, this invention forms a gas discharge display device provided with a front side substrate having a plurality of first electrodes and a back side substrate having a plurality of second electrodes, wherein at least the first electrodes or the second electrodes are formed from a resist made of an inorganic material by wet etching process.
Further, this invention forms a gas discharge display device provided with a front side substrate having a plurality of first electrodes and a first dielectric layer covering said first electrodes, a back side substrate having a plurality of electrodes and a second dielectric layer covering said second electrodes and a layer of an inorganic material layer interposed at least between said first electrodes and said first dielectric layer or between said second electrodes and said second dielectric layer, wherein said first electrodes or said second electrodes are formed by wet etching process.
Since a resist formed in the above-mentioned manner by forming an inorganic material into a film by sputtering or evaporation method has an increased adhesiveness to electrodes as compared with conventional resists made of organic material, such a resist is prevented from the corrosion by etching solution at the resist interface and thereby the breakage of wiring can be suppressed.
Further, if an inorganic material is used as resist, such a resist does not require so much consideration for etching damage as in the use of conventional resists made of organic material, so that an etching solution facilitating the control of etching quantity can be used, and the breakage of wiring due to side etching occurring in the conventional technique can be prevented by the use of inexpensive inorganic material. That is, as the inorganic material, ITO, SiO2, Nixe2x80x94Cr and the like can be used, for instance.
Further, since the inorganic material layer is lessened in reactivity with electrodes and dielectric layer, the inorganic layer may be made to remain between the electrodes and dielectric layer instead of releasing the inorganic layer, and this makes it possible to prevent the corrosion of electrodes and breakage of wiring due to the reaction between electrodes and dielectric layer.
For forming a resist by the use of an inorganic material layer, any means such as photolithography, blaster, laser and the like may be used.
In order to achieve the object mentioned above, this invention forms a resist by means of blaster. Thus, the gas discharge display device of this invention comprises a front side substrate having a plurality of first electrodes and a back side substrate having a plurality of second electrodes, wherein at least said first electrodes or said second electrodes have thereon a material layer formed by means of blaster and said first electrodes or second electrodes are formed from said material layer by wet etching process. In this case, the material layer serves as a resist for the first or second electrodes.
For forming the material layer, it is necessary to form a protecting layer functioning as a resist for said material layer. Since this invention forms the material layer (resist) by means of a blaster, etching solution does not permeate the interface between the protecting layer and the material layer, which lessens the risk of forming defects in the material layer (resist). This has made it possible to carry out the wet etching on a material having only a small number of defects and therefore to suppress breakage of electrodes. In addition, fabrication of a resist by means of blaster can be achieved in a short period of time at a low cost.
It should be additionally noted that, if the material layer is formed by means of laser instead of blaster, the formation of protecting layer necessary to the blaster process is unnecessary, due to which electrodes can be formed without photolithographic process and therefore the electrode-forming process can naturally be shortened to a great extent. In such an embodiment, the use of mask for forming an electrode pattern is unnecessary. Further, since in this case the material layer (resist) is formed without photolithographic process, a partial removal of the material layer by means of laser is enough for obtaining a desired pattern, which makes it possible to decrease the number of defects in resist extremely.
In these cases, the material layer (resist) may be made of any of organic material and inorganic material.
Further, in the case where blaster is used, the same fabrication as achievable by means of laser can be achieved by throttling the nozzle.
Moreover, the same processing as in the case of using a laser is possible even if the material layer (resist) is subjected to mechanical cutting to obtain a desired electrode pattern.